Charge collection in hydrogenated amorphous silicon (a-Si:H) radiation detectors is improved for high LET particle detection by adding thin intrinsic layers to the usual p-i-n structure. This buried p-i-n structure makes it possible to apply higher bias, and the electric field is enhanced. When irradiated by 5.8-MeV α particles, the 5.7-μm-thick buried p-i-n detector with a bias of 300 V gives a signal size of 60000 electrons, compared to about 20000 electrons with the simple p-i-n detectors. It is noted that the capability for tailoring the field by inserting doped layers or a-Si alloys with different bandgaps opens a way to come interesting devices. For example, controlled avalanche multiplication may become possible in the central intrinsic layer when it is sandwiched by heavily doped layers and separated away from the metal surfaces to avoid the microplasma breakdown